In the prior art, single jet nozzles or arrays of jet nozzles which, for example, may be used in ink jet printers, are approximately tubular in shape. These nozzles are formed by drilling holes in plates by mechanical or electromechanical means, by the use of an electron beam or laser or the like. The plates, for example, are made of stainless steel, glass or quartz, vitreous carbon, jewels such as sapphire and the like. The technique set forth above for forming nozzles or arrays of nozzles suffer from at least some of the following disadvantages, namely: (1) holes are formed one at a time, (2) control of the individual size and shape of nozzles is relatively poor; (3) fabrication of arrays of such nozzles is even more difficult, with attendant nonuniformity of hole size, shape and spatial distribution of the array.
In ink jet printing applications, a jet of ink is formed by forcing ink under pressure through a nozzle. The jet of ink can be made to break up into droplets of substantially equal size and spacing by vibrating the nozzle or by otherwise creating a periodic pressure or velocity perturbation on the jet, preferably proximate to the nozzle orifice. Printing is effected by controlling the flight of the droplets to a target such as paper. Important characteristics for ink jet printing applications are the size of respective nozzles, spatial distribution of the nozzles in an array, and the means for creating the periodic perturbations on the jet. Such factors affect velocity uniformity of fluid emitted from the respective nozzles; directionality of the respective droplets, that is, the directional alignment of the respective fluid streams with respect to parallel alignment; and breakoff distance of individual droplets, that is, the distance between the exit aperture of a nozzle and the position at which a droplet is formed.
According to the present invention, a jet nozzle or an array of such nozzles having appropriate jet orifice characteristics are fabricated from a semiconductor such as a single crystalline region of silicon by chemical etching techniques. Etching technology suitable for establishing structures of a given geometry in single crystalline silicon include U.S. Pat. No. 3,770,553, issued Nov. 6, 1973, which is directed toward a method for producing high resolution patterns in single crystals of silicon. There is, however, no teaching in the referenced patent concerning the use of the disclosed etching techniques for etching completely through a substrate of silicon or for fabricating jet nozzle structures in silicon.
Also according to the present invention, individual nozzles or an array of such nozzles are batch fabricated easily due to the crystallographic perfection of the starting material, namely the semiconductor used, and the selectivity of the etchant. There is a high degree of control of nozzle size resulting from precise control of processes used in fabrication, namely the formation of openings in thin films by photolithographic techniques and control of etch rates of semiconductor materials as a function of crystallographic orientation; and etching characteristics of anisotropic etching solutions as a function of their composition, temperature and the process environmental characteristics.
The fluid flow properties of the nozzle of the present invention are superior to those of pipes due to the minimization of wall effects. The wall effects are minimized since the nozzle according to the present invention is tapered from the entrance orifice to the exit orifice. The superior flow characteristics result in more uniform distribution of velocity across an array of jets operating from a common manifold.
Another advantage of the nozzle of the present invention is that inspection of a given nozzle may be accomplished visually, and such inspection is sufficient to anticipate the performance of the inspected nozzle. That is, the nozzle is inspected for orifice size and integrity of the structure without having to actually check the performance of the nozzle in an ink jet printer. In tubular shaped nozzles it is difficult, if not impossible, to see inside the nozzle.
The nozzle of the present invention may pass fluid in either direction, but in the preferred mode of operation fluid flow is in the direction of the larger opening to the smaller opening of the nozzle which results in less pressure drop.
The directionality of the jet is closely related to the directions in the crystallographic planes of the substrate material resulting in more uniform directional characteristics for an array than might otherwise be achievable.